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Why is it more common for consumer level FDM printers to move the extruder on the Z-axis (For example, the Ender 3) while the bed remains at a fixed height, than to have a bed that moves up and down on the Z-axis?

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  • $\begingroup$ if the nozzle is crooked it's no big deal. if the bed is crooked, it's a very big deal. $\endgroup$
    – dandavis
    Jun 9 at 2:08

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The reason is economics, building cheap printers for the masses requires the use of as less material as possible; this keeps the price down.

A bed that moves up and down requires a sturdy construction and usually more and more expensive materials.

If you look at the Prusa i3 style printer, the bed moves in Y direction while the X-Z is a single plane perpendicular to the Y-axis. This allowed printer designs to have a single upright frame made from acrylic (not the best solution, but cheap) or steel plate (expensive due to the cutout and waste material) or aluminum profiles (value for money solution). If you need the bed to go up and down, you need to constrain the X-Y plane high above the build plate (e.g. Ultimaker printers, Hypercube, etc.); this requires a stiff frame and hence more material.


Do note that e.g. the Voron 2.4 although a boxed up printer, has a fixed bed and a moving X-Y plane. This requires even more materials and is even more expensive.

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  • $\begingroup$ Building the printer upside down avoids a big part of this constraint. See for example the Positron V3. $\endgroup$ Jun 8 at 12:33
  • $\begingroup$ @R..GitHubSTOPHELPINGICE As seller of such a concept I would be concerned on supporting my community with prints not sticking to the build plate... ;-) (Thanks for the reference though!) Furthermore this concept uses linear rails which are very expensive compared to aluminum profiles, plate steel or acrylic, especially the quality ones. $\endgroup$
    – 0scar
    Jun 8 at 14:42
  • $\begingroup$ FWIW I think the back-and-forth motion of a bed slinger is probably more of a problem for adhesion than gravity. $\endgroup$ Jun 8 at 18:24

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